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Problems prone to loop resistance tester testing

time:2020/11/3   source:华天电力  reading:255 time

The loop resistance tester (also called contact resistance tester) designed according to the traditional design principle found a common problem when it was tested in the field. When the voltage connection circuit of the tester is poorly connected or open, the tester will also display a value. At this time, the following situations will occur:

(1) The voltage loop is open and there is no strong electric field interference at the test site. In this case, since the differential mode voltage input by the amplifier is basically 0, the test value displayed by the instrument is close to 0. If the tester has enough field test experience, it can judge the abnormality of the test line of the meter voltage loop and return the meter voltage. After excluding the abnormal test path, the final correct test result can be obtained.

Insulation Resistance Tester (3).png

(2) The contact of the voltage circuit is poor. In most cases, the terminal of the circuit breaker will produce an oxide film or oil film on the outer surface of the terminal after a long time operation. When the voltage test clamp of the circuit resistor is clamped on such a terminal strip, there may be a bad contact. When the voltage test clamp itself also generates a certain contact resistance, the contact resistance value is the same as the internal resistance value of the voltage sampling circuit. Will have a serious impact on the test results.

(3) The voltage circuit is open or poorly connected (when the circuit is open, the contact resistance r1 is infinite), and there is strong electromagnetic interference at the test site, such as a live bus. At this time, the live bus uses air as the medium to pass the capacitor, which interferes with the two voltage test lines of the tester. Due to interference, there are two voltage collection lines of the loop resistance tester. The differential mode voltage appears at the end.

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